Numerical Investigation of RC T-Beams Strengthened with Polymer-Modified Mortar and Embedded Steel Bars Under Earthquake Excitation

Near-fault earthquakes generate pulse-type ground motions that impose concentrated displacement demands on RC members, often leading to rapid degradation in stiffness and localized damage to negative-moment regions of T-beams. Although polymer-modified mortar (PMM) overlays with embedded reinforcement have demonstrated improved behavior under monotonic and cyclic loading, their response under seismic inputs with different characteristics remains insufficiently clarified. This study presents a parametric numerical investigation of RC T-beams strengthened with PMM overlays and embedded D13 and D16 steel bars and subjected to representative near- and far-field earthquake excitations. A three-dimensional nonlinear finite element model was developed and qualitatively validated against previously reported monotonic and reversed cyclic experimental results, with close agreement in the strength development and failure characteristics. The validated model was subsequently used in nonlinear time-history analyses. Under near-fault excitation, strengthening increased the peak load capacity by 52.40% (D13) and 73.30% (D16) relative to the control beam. For far-field motion, capacity gains of 53.77% and 65.85% were obtained, respectively. Near-fault input created pronounced localization in the compression zone, whereas far-field excitation resulted in more distributed cyclic deterioration. PMM strengthening substantially enhanced the flexural resistance and crack control, underscoring the importance of explicitly considering ground-motion type in performance-based seismic retrofit design.